This invention relates generally to a fluid tempering valve and more particularly to a tempering valve which accurately controls the temperature of a fluid at both high and low flow rates.
Tempered fluid mixing systems are used in a variety of commercial and industrial applications, for example, in gang showers. A typical system includes a thermostatic mixing valve or tempering valve which automatically blends hot and cold water supply streams to produce a mixed water output stream having a selected temperature. This tempered water is supplied through a common manifold to a plurality of fixtures such as shower heads.
Such tempered water mixing systems must be able to maintain the desired temperature regardless of the flow rate demanded. For example, a system could have a single fixture in use, or more than 20 fixtures could be in use simultaneously. It is difficult to design a tempering valve which accurately maintains a set temperature at widely varying flow rates. Attempts have been made in the prior art to provide accurate mixing at all flow rates. For example, some systems use a pair of mixing valves, one sized for a low flow rate and the other sized for a high flow rate, connected together with a pressure regulating valve or check valve between the outlets of the two mixing valves. However, when the larger valve does open, it is still only flowing a small percentage of the total flow. Such a system tends to have a “dead zone” of intermediate flow rates where the tempering is inaccurate. Accordingly, there is a need for a fluid tempering valve which accurately controls temperature at both high and low flow rates.